Preparation of olefins



DILUENT Feb. 18, 1958 A. l. M. KEULEMANS ETAL 2,824,148

PREPARATION oF OLEFINS Filed May 1'7, 1954 QUENCH FLUID ARIEN KwANTEs BWM M THEIR AGENT United States Patent O PREPARATIN F LEFBS Aloysius Ignatius Marie Keulemans and Arin Kwantes,

Amsterdam, Netherlands, assignors to Shell Development Company, New York, N. Y., a corporation of Delaware Application May 17, 1954, Serial No. 430,404

Claims priority, application Netherlands May 20, 1953 9 Claims. (Cl. 260-683) This invention relates to the preparation of oleiins, and particularly to the production of olens by the cracking of high boiling hydrocarbons.

It is known to prepare olens by thermal cracking, in the vapor phase, of high boiling hydrocarbons, or mixtures containing them. As starting material hydrocarbons oils with high molecular weight are used, which boil below about 450 to 500 C. However, it has hitherto been impossible to use in such vapor phase cracking processes higher boiling and less expensive initial material-s, such as residues which boil above 450 C. and are obtained when distilling petroleum or petroleum products, on a technical scale, since such initial materials during the required heating to cracking temperature and in the cracking process itself give rise to the formation of large quantities of carbonaceous deposits which tend to clog the cracking equipment.

In such thermal cracking processes heating of the starting material generally takes place indirectly, the heat required to raise the material to be cracked to the cracking temperature being supplied through a metal wall. This procedure, however, involves serious drawbacks. Thus very heavy demands are made on the material of the wall through which heat transmission is effected, especially when cracking is carried out at very high temperatures, for example 600 C. or even higher, and to this end special types of steels are required, which are costly. Another drawback is that-especially when it is desired to obtain high yields of nonbranched oleins from starting materials containing predominantly normal paraiiins-the time required to raise the material to be cracked to the cracking temperature should be so selected as to be as short as possible to avoid undesirable changes in the initial material, and that when high temperature gradients are employed to this end, there is the danger of overheating the starting material, with the result that nevertheless undesirable reactions may occur.

These undesirable reactions consist in a structural change of the hydrocarbon molecule, for example, a skeleton isomerization in the case of n-paraflins. Since such isomerizations increase as the temperature at which evaporation of the starting material is carried out is higher, and are also strongly catalyzed by carbon deposits, they are more pronounced with higher boiling initial materials than with lower boiling ones. Furthermore, the conventional recycling of non-cracked material, whereby this is thus repeatedly raised to a high temperature, is accompanied by a considerable decrease in the quality of the initial material.

In the case of cracking lighter hydrocarbons, such as ethane and the like to produce ethylene and the like, and such as lighter and readily vaporizable hydrocarbon distillates, `such as naphtha or gas oil to produce gasoline and gaseous hydrocarbons, including olefins such as ethylene, it has been shown that the preheated hydrocarbon feed material can be effectively heated by admixture with a large proportion of superheated steam (l700 F. or

higher) to an effective cracking temperature. (King and Warburton, Petroleum Processing, November 1952, pages rerice 16444; Carpenter and Fowler, Petroleum Rener, volume 3l, No. 4, April 1952, pages 148-9.) However, the pro-` duction of the large quantities of high temperature superheated steam requires heat transfer through the walls of the tubes of the superheater.

Various proposals have been made for the use of circulating masses of particulate refractory material, as in Jpebble heater and reactor" systems and the so-called thermofor process, for the thermal cracking of various petroleum materials to produce gasoline, olens, aromatics, and the like, `wherein the necessity of transferring heat to the reactants through a metal wall is obviated. it has also been proposed to utilize iluidized systems of heatcarrier refractory materials yfor the pyrolysis of hydrocarbonaceous materials.` However, none of these methods are entirely satisfactory, particularly for the cracking of high boiling hydrocarbons for the production of olefins.

It has also been proposed in some earlier patents, e. g., U. $1,274,976 as well as some more recent patents, e. g., U. S. 2,587,703, to provide the heat necessary to maintain the desired `temperature necessary to effect an efficient endothermic cracking reaction, by mixing the material being processed with a controlled proportion of oxygen, as air, to effect the oxidation of a part of the material in an exothermic reaction. However, the operations of even this latest development of the so-called autothermic process leave considerable to be desired, possibly because of some importantdiiferences in the factors which determine the optimum conditions for the exothermic oxidation and in the factors which determine the optimum conditions for the thermal cracking to produce the desired olens.

It has now been `found that products rich in olens may be prepared most advantageously, while avoiding drawbacks of previous methods, by bringing high boiling hydrocarbon mixtures, containing less than 25% by weight of aromatics, very quickly to a temperature of not lower than 500 C. by direct heating, effected by completely burning, in the atmosphere of the material to be cracked, a part of the said material in a relatively small heating zone which precedes the actual cracking zone :and in which there is an` oxidation-,promoting solid, and then passing the vapor mixture eiuent from the heating zone through the cracking zone.

It has been found that when proceeding in thi-s manner the material to be cracked is raised so quickly to cracking temperature that undesirable changes in the initial material` and side reactions may be entirely or practically entirely avoided.

As already indicated, it is true that cracking processes have been known before in which direct heating was applied by burning a part of the material in the atmosphere of the material to be cracked, but it has been found, according to the present invention, that in order to obtain products with a high content of oleiins, particularly higher straight chain olens, it is necessary to carry out this direct heating in the presence of an oXidation-promotform water, carbon dioxide and/or carbon monoxide and the heat] evolved by `this exothermic combustion very quickly raises the temperature of the entire mass of the mixture, preferably in a fraction of a second, to cracking temperature, i. e., to at least 500 C.

Combustion may be eiected by any suitable gas which sustains combustion, such as oxygen or free oxygen-containing gases, particularly air, or other gases having an` oxidizing effect, such as nitrogen oxides or ozone, or

3 mixturesthereof. The-partofthe starting material'which is burned will vary with the cracking temperature to be applied and the degree of cracking. In general combustion of not more than about to 15% by weight of the supplied material willsutlice.

Examples of suitable substances'which promote oxidation include'those having aY largeactive surface area, for instance, an areaof more than 40 square-metersfper gram, such as activated alumina; bauxite, silica gel, titanium oxide, cerium oxide, thorium.oxide,` chromium trioxidevanadium pentoxide, oxides of1 cobalt or manganese, or mixtures or: combinations of two or more of these substances. It is preferable to useV a strongfoxida-k tioncatalyst, for example, vanadium pentoxide, which is suitably applied to a carrierrsuchas activated alumina,

silica gelfragments madefrom bauxite, silicates, etc.

The use ofsuch substances having .a large active surface area greatly assists combustion and ensures extremely rapid and uniform heat transmission to the hydrocarbon material .passing through the heating zone while moreover the capacity. of this zone, as compared to that of the ad-y jacent but distinct cracking zone, maybe small, sothatV the residence time of the materialin the heatingzonel under highly active oxidizing conditions may be only a small fraetionof the residence time of the material in the crackingV zone under essentially non-oxidizing conditions. The ratio ofthe capacity of the heating zone to the cracking zone generally lies between about 1:8 and 1:100,

aparticularly eifective ratio being between about 1:15' and 1:50. The heating andthe cracking spaces can be madefrom comparatively cheap materials, such as ordinary steel, theheating space being'conveniently provided on its insidev with arefractory lining.

The hydrocarbon vapors heated to cracking temperature inthe heating zone are passed directly and immediately intothe cracking zone, in which the hydrocarbonr molecules by a purely thermal vapor phase cracking decompose into smaller'fragments, products with a high olefincontent beingj thereby produced. Y

As starting material for the process of the invention, any type of high boiling hydrocarbon mixture (i. e.,

boiling above about300 C.), which may be of natural or.I synthetic origin, may be used, provided it does not .contain more than 25%y by weight, and preferably amaximum of by weight, of aromatics. Initial materials having a higher aromatic content have been foundito be unsuitable because they causepronounced carbon 'deposits to form in the. heating and. cracking zones, .which give rise to' serious interruptions to operation.

The aromatic content is readily determined by per@ colating a sample ofthe hydrocarbon mixture over silica gel .and then, desorbing: the non-aromaticsV by Washingfthe silica gel.with.a. low boiling. saturated hydrocarbon, for example n-:hexane,.after which the portion of the sample left7 orr the silica gelis regarded. asy aromatics.

Thefcomposition ofthefnon-aromatic'part of the initial material,. which may consist of normal: parains, isoparafns and naphthenes, is ofA secondary importance if it: isl intendedi toV prepare mainly olefins with lower molecular weight, that is to say, with less than 6 carbon atoms per molecule. However, this is not the case when it-is desired to produce mainly higher olens. In order to' obtaina cracked product with a high content of higher olefins, in particular those. with a straight chain, it has been foundto be desirable that the starting material should have a content of higher paraffin molecules or radicals of more than 40% by weight, preferably more than 60% by weight. These parans may not only occur as normal alkanes butalso intheform'ofstraight chains which are boundtohydrocarbons ofdifferentstructure, for instance as in a higher n-alkylnaphthene.

Examples' of suitable initial` materials are. high' boiling, mineral oi-l :fractions-poor. in aromatics, or Fischer-Tropsch higher. hydrocarbons,V paratn waxdistillates or other material rich in paraffin wax such as paraffin wax obtained when dewaxing lubricating oils, and the like.

A special advantage of the process of the invention is that it provides a method whereby cheap initial materials which are abundantly available may be used as starting material, such as residues boiling above 450 C. which are obtained when distilling mineral oils or mineral oil products, and which could not be processed'inthe vapor phase cracking processes heretofore employed.

,The starting material to be converted may. be. conveniently preheated, decomposition with the'formationof carbon deposits being preferably avoided. If the-starting material is not liquid, owing to the presence of normally solid parans, it must be sufliciently preheated to liquefyxit.

The temperature at which the starting material is heated in the heating zone and also theL residence time of the vapor mixture effluent from that zone in the cracking zone will depend on the natureof: the olelins whichare desired to be prepared.

When it is desired to produce mainlyvlower oleins, suchkr aslethene, propene and butenes, generallyv crackingtemperaturesinthe range from 650 C. to 900 C., preferably' from 700 C. to 800 C., are-employed and residence' times inthe cracking space varying'from 3 to 0.001` secends, preferably from l' to-0.-2` second, areused. Accordingly as the crackingtemperature is-selected"higher, the,

residence time shouldbe shorter to obtain' optimalresults. In actual practice there is a ccrtainlimit-tothe cracking temperature which should be as high as possible;

'For the production of higher olens, such as' products rich-in straight-chain olens with more than 6carbon atoms; lower cracking temperatures, namely, between. V500 C and 650 C., preferably between 550 CL andf 600 C., are used while in that case residence times in the cracking space vary from about 20 to 0.5 seconds,.`

preferably from aboutS to l seconds.

With aV given system the residencek time may be adjusted, within the desired limits by means of the throughput rate.v

The processaccording to the invention, which is usually;

applied under atmospheric pressure, but which may be performed at a higher or lower pressure as well, can,.for instance, be carried out by passingv the material to be cracked, preferably in a preheatedstate,.in.conjunctionr with the oxidizing gasand any diluent that maybe applied, atthe` desired rate through the-heatingzonei-containingi afixedr substance having a large surface area andi-beingan'.4

oxidation-promoting solid, afterr which the vapor. mixture thush'eated to cracking temperaturel is passed'into thel cracking 'zone in which'it remains forA the required time,

the Vreaction producteluentifr'omthe .cracking zone being thenquickly cooled. or quenched; whichisrconveniently eifected by direct. contact with: a`coolant,.forinstance, water,,cooledinertrefractory pebbles, cooled inertv finely divided refractory material ina fluidized bed, and thelike:

Depending on the reaction conditions applied, the processrof the.` invention yields products which are rich in` olens andv consist mainlyofl lower olefins such4 as ethene, propene, butenes and the like (which-may be' convertedintovaluable derivatives'of'various kinds, for example, saturated or unsaturated halohydrocarbons, alcohols, etc.) or consist to a large extent of higherolens which mayalso be used for preparing valuable derivatives; Thus-the higher straight-chainolefins, forexample, those boilingbetween-about` C. and 300 C., are an excel-4 asa-4,148

lent starting material for the production of secondary sul furie acid alkyl ester salts, for instance, secondarysodium alkyl sulfates having an excellent detergency, while the higher branched oleiins, which are also formed, are, for example, suitable for use as initial material for preparing alkyl aryl sultonates possessing also good surface-active properties. Y

Another iield of application of the higher olens obtained by the practice of the invention is the production of products intended for use as lubricating oil additives, for instance, calcium alkylsalicylates.

The process according to the invention will be further described by means of the drawing which schematically illustrates a preferred mode of operating the process. A hydrocarbon feed which may suitably be a paranic oil containing about by weight of aromatics and boiling above 500 C. is passed by line 11 through preheating zone A, in which it may be preheated to 100 C. From zone A, the feed passes in liquid phase through line 12 into heating zone B. Combustion sustaining gas enters the system through line 13 and header 14. The gas, which may be, for example, air or oxygen, may be passed directly into heating zone B by opening valve 15 in line 16 or it may be admixed with the hydrocarbon feed ahead of the heating zone by opening valve 18 inline 19 to introduce the gas into line 12. The section of line 12 from the intersection with line 19 to the point at which it enters the heating zone may represent a suitable oil burner. A diluent, such as steam, may be added, if desired, by introducing it through line 20 into header 21 from which it may pass to line 12 by opening valve 26 in line 22 or it may pass into heating zone B by opening valve 28 in line 24. There are known to the art numerous methods for introducing a liquid or vaporous oil feed into a combustion zone, either in previous admixture with combustion supporting gas or in such a manner that the oil and com# bustion supporting gas are admixed in the combustion zone, and either with or Without the addition of diluent gas. Heating zone B is filled with a bed of particulate oxidation promoting solid, 30, e. g. a catalyst consisting of 95% by weight of activated alumina and 5% by weight of vanadium pentoxide. The catalyst bed may be separated from the cracking zone C by a separating member 31 which may be a Wall with suitable openings to permit passage of the mixture of oil vapors and combustion gases from zone B into Zone C. Cracking zone C will ordinarily be an open space confined by a wall 32 of material resistant to moderately high temperature, e. g. ordinary steel. Similarly, heating zone B will be coniined by a wall of high temperature resistant material, e. g. ordinary steel which may be lined with a refractory material such as re brick. The mixture of combustion gases and oil vapors is retained in the cracking zone C for a sufficient length of time, in the range stated, to produce a substantial amount of olefinic material. The reaction mixture is then withdrawn through line 34, Where it is immediately quenched in quenching zone D by injecting a quench fluid through line 35. The quench fluid may be, for example, liquid water. The quenched mixture is then passed through line 34 to suitable condensation, separation and recovery equipment, not shown, to recover ultimately as product of the operation olenic materials such as normal alkenes.

The process according to the invention will be further illustrated by reference to some examples.

Example I A parafnous oil residue having an aromatic content or" 15% by weight and boiling above 500 C. was preheated to 100 C. and the material thus melted was passed, at the rate of 600 grams per hour, together with 100 liters of oxygen and 360 grams of water per hour, through a heating space iilled with 100 ml. of catalyst Consisting of 95% by weight of activated alumina and 5% by weight of vanadium pentoxide, and which had been preheated to 400 C.

The temperature in the catalyst bed rose to 750 C. The parafiinous residue, of which 9% by weight was burned to form waterand carbon dioxide, was thereby heated in a period of 0.05 second from 100 C. to 750 C. The vapor mixture ilowing from the heating space passed through a cracking space having a capacity of approximately 800 ml., the residence time therein being 0.4 second and the temperature having dropped to about 700 C. when the effluent iiowed out. In this case there was obtained a product of which 70% by weight boiled below 30 C. This product boiling below 30 C. amounted to 61% by weight, calculated on the starting material.

The ethene-ethane fraction was 90% by volume ethene and 10% by volume ethane. The propene and the butene fraction were practically 100% oleiins.

Calculated on initial material there were formed: 7% by weight of methane-hydrogen fraction, 26% by weight of ethene-ethane fraction, 15% by weight of propene fraction and 13% by weight of butene fraction.

Example II A parainous oil residue boiling above 500 C. and having an aromatic content of 10% and consisting for the rest mainly of branched paraiiins, was preheated to 100 C. The starting material, thus melted, was passed at the rate of 500 grams per hour, together with liters of oxygen and 300 grams of water per hour, through a heating space iilled with 100 ml. of a catalyst consisting of 95% by weight of activated alumina and 5% by weight of vanadium pentoxide and which was preheated to 400 C.

The temperature in the catalyst bed rose to 620 C. Of the hydrocarbon material, 10% by weight was burned to form water, carbon dioxide and carbon monoxide. The temperature rose thereby in 0.05 second from 100 C. to 620 C. after which the mixture was kept for a further 1.5 seconds in a cracking space having a capacity of about 3 liters, from which it was withdrawn at a temperature of approximately 600 C.

Of the product obtained a part corresponding to 26% by weight, calculated on starting material, boiled below 30 C. The portion boiling above 30 C. yielded) on distillation 17% by weight (calculated on starting material) of a distillate, boiling between 30 C. and 300 C. This distillate contained 13.7% by Weight (calculated on starting material) of a fraction boiling between 145 C. and 300 C. This fraction had a bromine number of 81 corresponding to a mono-olefin content of 78%; by weight, the content of olens with straight chain being 52% by weight. This fraction was suitable for use as initial material for preparing secondary sulfuric acid alkyl ester salts.

Example III As starting material use was made of a paraliinous material boiling between 350 C. and 450 C. (obtained by dewaxing a light lubricating oil fraction) having an aromatic content of 3% by weight and an n-paraiin content of 85% by weight and for the rest consisting of naphthenes and isopara'ins.

This material was preheated to 100 C. and passed at the rate of 500 grams per hour, together with 80 liters of oxygen and 300 grams of water per hour, through a heating space filled with 100 ml. of a catalyst consisting of by weight of activated alumina and 5% by weight of vanadium pentoxide.

The temperature rose thereby in the catalyst bed to 620 C. and 10% by weight of the hydrocarbon material was burned to form water, carbon dioxide and carbon monoxide. The temperature rose in this case in 0.05 second from C. to 620 C. after which the vapor mixture was kept for a further 1.5 seconds .in a cracking space having a capacity of approximately 3 liters, from whiclrit'was 'withdrawn' at: a Vtemperature` of l"600" C.

Of `the product obtained a part corresponding vto 25% by weightsof vthestarting material-boiled below *30 C:

The portion boiling-above30 C. gave ondistillation 18% by weight (calculated on starting material) of a distillate boiling between 30 C. and 300 C; This distillate contained 14% by weightA (calculatedon starting material) `of a fraction boilingbetween 145 C. and 300 C, with a bromine number of 85 corresponding to -a mono-olefin content'of 87% by Weight,` while the content of straight-chain oleiins amounted to 75% by weight. This-fraction was suitable for use as initial material for preparing secondary sulfuric acid'alkylester'salts.A

We claim as our invention:

1.V A process for preparingoleiins by cracking high boiling hydrocarbons while suppressing side reactions which comprises passing a high boiling hydrocarbonY mixture containing less than 25% by weight of"aromatics together with a minor proportionof combustion sustaining gas through a relatively small heating zone containinga bed of particulate oxidation-promoting solidrjunder conditions for essentially complete combustion ofa portion of the hydrocarbon mixture and for quickly raising the temperature thereof to at least 500 C., and immediately thereafter passing the resulting mixture@ emuent from the heating zone through an unobstructedcracking zonewhoseV capacity is atleastfeight timesthat of said heating zone for a short residence time therein wherein essentially onlyvthermal cracking conditions are maintained, cooling th'eeluent cracked products from the cracking zone. below crackingl temperature, and-'recovering oleins-from the product. y g

2. AV process according to-claim'l wherein said-conibustion sustaining gas is free oxygen. 1

3. A.- process according to claim 2 wherein saidf oxidation promoting-solid". comprises vanadium pentoxide' supported'on a carrier-having a-large-activesurface area.

4. A process according to claim 2, wherein the heating 0.001 seconds said recovered olens being mainly normally, gaseous olens.

6. A- process according to claim 4, wherein the temperature -to which the hydrocarbon mixture is heated in the heating zone is between 500 C. and 650 C. and the residence timefin the cracking zone is between about 20 and 0.5 seconds-said'recovered'olens being mainly nor'- mally liquidfolens.

7. A process-according to claim 6, wherein the hydro.- carbon. mixture contains more than 40%-by weight of parafnsand no vmore than 15% by weight of aromatics.

8. A process accordingl to claim 2, wherein the high boiling hydrocarbon islaresidue boilingabove 450 C. and obtained-,in the-distillation-of mineral oils.

9. A process according to claim 2, wherein the heating andfcracking`r are etected in the presence of added steam.

References Cited in the tile of this patent UNITED STATES PATENTS 1,295,825- Ellis Feb. 25, 1919 1,597,798- James- Aug. 31, 1926V 1,935,148 Dilbbs Nov. 14, 1933 2,371,147' Burk Mar. 13, 1945 2,394,849 Doumani etal Feb. 12, 1946 2,520,149 Keeling Aug. 29, 1950 2,587,703! Deanesly Mar. 4, 1952 2,595,254v Hennninger` May 6, 1952 2,766,308 Watkins Oct. 9; 1956 

1. A PROCESS FOR PREPARING OLEFINS BY CRACKING HIGH BOILING HYDROCARBONS WHILE SUPPRESSING SIDE REACTIONS WHICH COMPRISES PASSING A HIGH BOILING HYDROCARBON MIXTURE CONTAINING LESS THAN 25% BY WEIGHT OF AROMATICS TOGETHER WITH A MINOR PROPORTION OF COMBUSTION SUBSTAINING GAS THROUGH A RELATIVELY SMALL HEATING ZONE CONTAINING A BED OF PARTICULATE OXIDATION-PROMOTING SOLID UNDER CONDITIONS FOR ESSENTIALLY COMPLETE COMBUSTION OF A PORTION OF THE HYDROCARBON MIXTURE AND FOR QUICKLY RAISING THE TEMPERATURE THEREOF TO AT LEAST 500*C., AND IMMEDIATELY THEREAFTER PASSING THE RESULTING MIXTURE EFFLUENT FROM THE HEATING ZONE THROUGH AN UNOBSTRUCTED CRACKING ZONE WHOSE CAPACITY IS AT LEAST EIGHT TIMES THAT OF SAID HEATING ZONE FOR A SHORT RESIDENCE TIME THEREIN WHEREIN ESSENTIALLY ONLY THERMAL CRACKING CONDITIONS ARE MAINTAINED COOLING THE EFFLUENT CRACKED PRODUCTS FROM THE CRACKING ZONE BELOW CRACKING TEMPERATURE, AND RECOVERING OLEFINS FROM THE PRODUCT. 